import java.util.Date;

public class HelloWorld {

    public static void main(String[] args) {
        System.out.println(1234);

        /*String a = "hello Java";

        System.out.println(a);*/
        String s1 = "a";
        String s2 = "b";
        String s3 = "a" + "b";//被编译后，就是ab,"常量优化机制"，在常量池
        String s4 = s1 + s2; //String s4 = new StringBuilder().append(s1).append(s2).toString(); ==> new String(value, 0, count);
        String s5 = "ab";

    }
}
